1. Field of the Invention
The present invention relates to a vehicle seat (including an automotive seat) having a ventilation function. In particular, the invention is directed to a vehicle seat of this kind, which has ventilation portions defined at the regions adapted to be contacted by a seat occupant's back portion, buttock portions and thigh portions in order to prevent those seat occupant's body portions from becoming sweaty with perspiration.
2. Description of Prior Art
One example of conventional vehicle seats having a ventilation function is disclosed in Japanese Laid-Open Patent Publication 2012-115515 (hereinafter, “JP 2012-115515 A1”). This publication teaches provision of a three-dimensional air-permeable network cushion element in an urethan foam padding provided in a seat cushion of vehicle seat, at a location on which two thigh portions of a seat occupant are to be rested. The three-dimensional air-permeable network cushion element is formed by entangling a plurality of fibers of thermoplastic resin material with one another and thermally fusing them together at their mutually contacted points. Thus, many spaces among the fibers permit flow of air therethrough for sufficient ventilation at the region to be contacted by the two thigh portions of seat occupant in the seat cushion, thereby preventing the thigh portions from becoming sweaty.
Although not shown in the JP 2012-115515 A1 above, as any person skilled in the art will readily consider, the foregoing network cushion element for the ventilation purpose can be applied to a seat back of vehicle seat at one or more required regions to be contacted by a back portion of a seat occupant, in order to prevent the back portion from becoming sweaty. However, the inventor and assignee of the present invention have not found any prior art material which exactly shows use of the similar network cushion element in the seat back for ventilation purpose.
According to the JP 2012-115515 A1, the three-dimensional air-permeable network cushion element is disposed in an entire forward half area of the seat cushion, as a result of which, a weight or load is applied from the seat occupant's thigh portions directly to that network cushion element. Hence, as the seat occupant has used the seat for a long period of time, the resiliency or repulsive forces of the fibers in the network cushion element become decreased more rapidly than thought, so that a cushiony touch of the whole network cushion element will soon be deteriorated to an unfavorable degree. Further, with the decrease of repulsive forces of the fibers, it is highly possible that the network cushion element will not maintain its original shape and thickness, and therefore will become settled downwards into a permanent depressed and thin state, which is “permanent settling” of the network cushion element. In other words, substantially the forward half area of the seat cushion may be subjected to downward perment settling and become small in thickness, which will impair the outer appearances of the seat undesirably. Also, most of the fibers in so depressed network cushion element will be squeezed and closely contacted with one another, as a result of which, the spaces among the fibers will be so narrow as to obstruct smooth ventilation of air therethrough. Thus, in this prior art, it is likely that a useful life of the seat will be shorten in terms of its ventilation effect as well as of its outer aesthetic appearance.